A variety of faults can damage fragile semiconductor devices. Current-based faults are of particular concern because these can permanently destroy an integrated circuit. Two important types of current-based faults are excessive current and reverse current. Excessive current can create excessive heat within the integrated circuit, and such heat can destroy transistors, diodes and other components in the integrated circuit. Reverse current occurs when an external device forces a current onto the integrated circuit. Reverse current can also destroy devices on the integrated circuit. Along with the destructive effects of current induced heat, reverse current can cause many semiconductor junctions within the integrated circuit that are normally reverse biased to become forward biased. The forward bias condition allows the reverse current to create damage in many parts of the integrated circuit. For example, these problems may occur in an integrated circuit that: (a) is part of a primary device, such as a smart phone or computer; or (b) provides power to an accessory device, such as a SIM card, a credit card reader, or other accessories.
Protection devices are often included at the accessory power output terminals of integrated circuits to prevent current based faults. One such protection device includes a switch device (such a high capacity FET) coupled between the output terminal and the integrated circuitry. Circuitry within the integrated circuit monitors the voltage drop across the switch. Under certain conditions, the switch opens to decouple the integrated circuit from the output terminal. This is an effective protection technique. However, when the decoupling occurs, the accessory temporarily shuts down and then must go through its start-up cycle. Interruption of the accessory process can severely affect device and system performance. In some normal operating conditions, sufficient current flow can flow through the switch to trigger the protection circuit and cause decoupling of the accessory, even when a true current fault has not occurred. Accordingly, the protection device should be triggered only for events that truly endanger the integrity of the integrated circuit.